LTM virtual server spanning

Hi Guys, Need advice on the impact if enabling or disabling Spanning under Virtual Server configuration? I read through the help section and also F5 article but still dont quite understand its usage. More for like ECMP routing??

 

https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/bigip-system-ecmp-mirrored-clustering-12-1-0/3.html

 

Many thanks, David Saw